AU673688B2 - Recovery of precious metals - Google Patents

Description

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AUSTRALIA

Patent Act COMPLETE SPECIFICATI ON

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: .r Names(s) of Applicant(s): TECNAV PTY. LTD.

Actual Inventor(s): Frederick TAYLOR Our Address for service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street MELBOURNU lustralia 3000 Complete Specification for the invention entitled: RECOVERY OF PRECIOUS METALS The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- I I I

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*9 9 *99* RECOVERY OF PRECIOUS METALS This invention relates to a method and apparatus for use in the recovery of precious metals. The invention principally i. concerned with gold recovery but, if required, it also enables recovery of other precious metals such as silver and platinum group metals.

Conventional gold recovery processes essentially involve recovery of gold present as discrete, identifiable particles. However, gold-containing ores and tailings also have the metal present in a diffused molecular or atomic form (herein "the diffused form"), although, this generally is not appreciated. Gold in the diffused form is not detectable by fire assaying, due to it being lost as an evolved gas, while it also does not report in aqua regia and cannot be detected by neutron activation. As a consequence, undetected but significant quantities of gold are present in ore tailings. Processing of ore, or reprocessing of tailings, for recovery of gold, thus occurs only if a sufficient level of gold is found to be 20 present as discrete, identifiable particles.

Gold and other precious metals present in an ore or tailings (herein "source material") in the diffused form has been found to be capable of recovery. However, recovery necessitates the source material being in a relatively low density pulp, such as of less than 15 wt% source material in water. Also, in such pulp, the source material needs to be finely divided, such that the source material is held in suspension. The source material can be of a particle size typical of tailings from 30 conventional gold recovery operations.

One procedure for recovery of gold and other precious metals from such low density pulp utilises ion exchange resin beads. Even with this procedure, a relatively low density pulp is necessary since, with higher density pulps, there is an unfavourable equilibrium between the quantity of precious metals in the diffused form taken up by the beads and the quantity transferred back to the source material. However, there are further problems in separating the beads from the pulp solids, and in separating the beads from pulp liquid, in an efficient 3114L 2 I, I 01 OCT '96 14:02 PHILLIPS ORMONDE -IT2PATRICK 9 manner which minimises mechanical damage to the beads and thereby enables them to be recycled. The resin beads are relatively expensive, and economic operation is possible only If they can be re-used in a sufficientl number of recovery cycles.

The present invention seeks to provide improved aplaratus for effecting o0 bead recovery for re-use. The invention E'so Is directed to providing an overall installation and a method for recovery of gold and, if required, other precious metals, utilising such apparatus.

In a first aspect, the invention provid.s a centrifuge, suitable for use in separating ion exchange resin beads from a process licuid, such as after separation of the beads and process liquid from a pulp, wherein the centrifuge has a bowl and a drive motor for rotating the bowl on an lupwardly extending central axis, and wherein the bowl has a peripheral wall which curves smoothly upwardly and outwardly from a basal section thereof and thelmotor is adapted to provide slow rotation of the bowl. While the motor may be operable to rotate the bowl at a substantially constant speed, it alternatively may b variable to enable variation of the speed of revolution of the bowl, Except where the peripheral wall is outward'/ stepped a short distance below the rim, the curvature of that wall is of a smoothly cuived parabolic form between the basal section and the rim. Where outwardly stepped, the peripheral 25 wall defines an outwardly extending annular flange and has a smoothly curved lower portion of parabolic form between the basal section anoi the flange and an upper portion of similar curved form between the flange and the rim.

The centrifuge typically is to receive, from above the bcwl, a feed of beads and liquid to be separated, For this, the centrifuge may have deflector moun' J axially above the bowl for guiding the feed as it flows into the ,owl. The deflector may be of conical form and mounted substantially co-axially a aove the bowl. The deflector preferably curves downwardly and outwardly to faci itate a smooth flow of the feed downwardly and radially outwardly into the bowl. The deflector may be rotatable such that initial circular motion is imparted to the feed flowing down the deflector, with rotation of the deflector being in the same d rection as the bowl.

The basal section of the bowl may define an outl t for liquid to be separated from the beads, The outlet may be defined oy a central weir which the liquid overflows. Preferably the weir is a substantially annular hub portion of the bowl which is substantially concentric with. but of lesser height than, the peripheral wall. The hub portion preferably is substantially cylindrical. The basal section of the bowl, between the hub portion and the peripheral wail, preferably is internally concave and curves downwardly and inwardly from the peripheral wall and then upwardly and inwardly to the hub portion.

The arrangement of the centrifuge is that, with feed of beads and liquid flowing into the bowl, and rotation of the bowl under the action of the motor, a separation is effected in that the liquid is discharged from the central outlet and the beads move outwardly and up the peripheral wall to discharge over an upper rim of that wall.

However, variations are possible in this overall system.

If the peripheral wall curves smoothly to its upper rim, it is desirable that the centrifuge be operated at a relatively precise minimum critical speed of revolution of the bowl. The critical speed w is determined by: w 2-Zg-H R where H is the nominal height of the peripheral wall and R is the radius of that wall at the rim. For speeds less than w, ,he beads do not rise to the rim while, for speeds too much in excess of w, excessive quantities of liquid also pass over the rim. Most ion exchange resins need to be kept moist so as to prevent their deactivation by oxidation, and a surface film of liquid is sufficient until the beads are contacted with further liquid.

Operation at or not too far in excess of the critical value of w retains such surface moisture without the effectiveness of separation being reduced by further S 30 liquid passing over the rim. However, it is desirable to o be able to effect such separation without the constraint of operating at or close to the critical value of w, and a modified form of bowl enables this.

In the modified form of bowl, the peripheral wall is outwardly stepped a short distance below its rim, by provision of an outwardly extending annular flange. The peripheral wall extends above the outer edge of the flange, to the rim. Intermediate the flange and the rim, the peripheral wall has a perforate band which retains the beads but allows an outward flow of liquid. With this 3114L 4 1 1 modified form of bowl, operation at higher speeds in excess of w is possible since, although such operation results in a mixture of liquid and beads moving up the peripheral wall, the beads pass across the perforate band so as to pass over the rim, while the liquid discharges through the perforate band. The mix of beads and liquid reaching the flange is accelerated radially across the flange, and this is found to achieve separation.

Where the bowl is of the modified form, the separation of beads and liquid can, if required, be effected solely at the perforate band. However, it is preferred that a partial separation is effected in this way, with the basal section of the bowl defining an outlet by which the remainder of liquid is separated, since this enables a substantially increased throughput. Where the bowl is not of the modified form but has a peripheral wall of uninterrupted parabolic form to its rim, such outlet in the basal section is necessary.

The rim of the bowl preferably is smoothly curved 20 outwardly from the peripheral wall. This facilitates [,outward acceleration of the beads, enabling them to overcome surface tension tending to adhere them to the bowl surface at the rim. Most preferably the bowl has a *"peripheral skirt which is inclined downwardly and 25 outwardly from the rim. Where the bowl is of the modified form, such skirt may extend above peripheral structure around the bowl which ensures isolation of beads discharging from the bowl from liquid discharging through S" the perforate band.

30 The centrifuge preferably has means operable to spray the beads with wash solution. The wash means is disposed around the bowl, outwardly from the rim, for discharging wash solution for contact with beads passing from the bowl. The wash means may be operable to generate 35 an annular curtain or spray of wash liquid from wash liquid discharge head or nozzles disposed around the bowl.

The centrifuge of the invention may comprise a single unit of the form described. Alternatively, it may be one of a plurality of similar units, in a vertical array. In the latter case, the bowl of each unit may be 3114L 5

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rotatable under the action of a single motor providing drive to a shaft common to each bowl. The beads discharging from an uppermost centrifuge of the array, with wash liquid from that centrifuge, preferably pass to the next centrifuge, and so on through to the lowest centrifuge if there are more than two.

The centrifuge of the invention enables separation of beads and process liquid in a manner which is efficient and which minimises risk of mechanical damage to the beads. Typically, this separation occurs after the beads and the process liquid have been separated from a pulp of precious metal-containing source material. This latter separation also needs to be effected with minimal risk of damage to the beads, and the present invention also provides apparatus for this.

In a further aspect, the invention provides extraction apparatus. In this, suitable ion exchange resin beads are contacted with a pulp of source material, to enable the beads to take up precious metals in diffused form from the source material, and then separated from the pulp. The extraction apparatus includes a tailings tank for containing an aqueous suspension of the source material as a relatively low density pulp; an inlet to the tank for the supply of the pulp, with the inlet being S 25 within a lower region of the tank which is spaced above a *o base of the tank such that the pulp flows upwardly for discharge from an outlet at the top of the tank; an inlet to the tank for the supply of ion exchange resin beads, the beads inlet being at an upper region of the tank to C. g e S 30 enable the beads to settle under gravity through the pulp; mixing means operable to gently stir the pulp, to effect intimate mixing of the source material and beads; and discharge means by which settled beads are able to be separated from pulp and withdrawn from the tank. The discharge means includes an outlet in the base of the •tank, and an eductor by which the settled beads and liquid are able to be drawn from the tank via the outlet. The discharge means also includes, between the pulp inlet and the base, an inlet from which separating liquid is able to be supplied to the tank to maintain a body of separating 3114L liquid below the pulp, such that the beads settle in the separating liquid. The eductor thus is able to extract the separating liquid and beads therein as a mixture substantially free of source material.

The upward flow of pulp from the pulp inlet retards the counter-current settling of beads, and thereby increases the residence time of the beads in the pulp. As a consequence, the height of the tank can be substantially less than otherwise would be necessary; a tank of, for example, about 8 feet in height being practical. Stirring of the pulp enhances dispersion of the beads throughout the pulp and, hence, intimate contact between the beads and the source material. Stirring at about 1 rpm is found to be sufficient for this, and retains a relatively well defined interface between the pulp and the body of separating liquid.

In a process according to the invention, an aqueous pulp of source material, such as particulate tailings, is charged to the tailings tank of such extraction apparatus 20 and ion exchange resin beads are mixed with the pulp by gentle stirring. The tailings particles, although substantially more dense than the beads, are relatively fine and are retained in suspension. The stirring, such as with paddles, ensures that the settling beads and the tailings are intimately mixed, without substantial segregration, and avoids damage to the beads. The stirring, such as up to about 1 rpm or a little higher, is to maximise contact between the beads and tailings, without causing the beads and tailings to separate under S 30 prevailing forces. The upward flow of pulp ensures that the beads have a sufficient residence time in the tailings tank. Precious metal values such as gold, which are present in diffused form in the tailings pulp, are taken up by the beads and the beads and tailings subsequently are separated for recovery of those metal values.

S•The pulp supplied to the tailings tank preferably is of relatively low solids content, such as less than 15 wt% solids, and the pulp thus is readily able to be pumped to that tank. The pulp and separating fluid, such as water, are preferably simultaneously charged to the tailings tank 3114L 7 and, in one convenient arrangement, feed to the tailings tank is continuous.

The pulp preferably is discharged within the tailings tank via a circular manifold, with pulp passing to the manifold from a supply line through which it pumped from a tailings pulping tank. The separating fluid, preferably water, is pumped into the tailings tank, to maintain the body of separating fluid below the pulp and preferably provides a downward flow adjacent the base of tailings tank, towards the outlet in the base. The separating liquid preferably flows downwardly across a sloped base of the tailing tank, towards the outlet.

Discharge of separating liquid and beads from the outlet via an eductor minimises risk of mechanical damage of the beads, such that the beads are able to be recycled after separation and treatment for recovery of precious metals.

The beads may be supplied to the tailings tank in any suitable manner. However they preferably are supplied above the level of pulp in the tailing tank to maximise their residence time in that tank and thereby enable the beads to become fully loaded with metal values taken up from the pulp. The beads preferably are sprayed downwardly into the tailings tank, such as from a rotating .C *spray bar system above the tailings tank.

The ion exchange resin used for the beads may comprise resin which selectively takes up precious metals such as gold, in preference to other metals such as base metals. However, it is preferred to use beads of a less selective resin such that, on being mixed with the pulp, 30 they take up other metal values in addition to those of precious metals. In either case, it is highly desirable that the beads be kept wet at all stages, so as to avoid the risk of oxidation and loss of ability to take up metal values. They therefore preferably are supplied to the 35 tailings tank, and recycled, in a circuit in which they remain wet, although this is not necessary for some oxidation resistant beads now available.

The mixture of beads and liquid drawn from the tailings tank is passed to a centrifuge as detailed above, to effect separation of the beads from the liquid. Most 3114L 8 preferably the mixture is passed to a low speed cyclone device which is mounted above the centrifuge and is operable to effect a partial separation of the liquid.

The cyclone device has a containment vessel into which the mixture is received, such as via an inlet adjacent the base of the vessel. The cyclone acts to slow the velocity of the incoming mixture, enabling the Leads to settle, while this action is assisted by paddles which are rotated slowly. Some water discharges from the vessel from an upper outlet, while the beads and remaining liquid pass through an outlet in the base of the vessel, to the centrifuge. Operation of the centrifuge will be understood from the description provided above. The beads, on overflowing the centrifuge, preferably are contacted with cyanide wash solution with which they are passed to a cyanide treatment tank.

The beads passing to the treatment tank preferably are dispersed onto the upper surface of cyanide solution in that tank. The centrifuge preferably acts to spray the beads onto that surface, such as via a rotating spray bar. The arrangement of the cyclone and centrifuge is o such as to prevent water from the tailings tank passing into the treatment tank, so as to avoid undue dilution of S. the cyanide solution.

The centrifuge most conveniently is mounted above the treatment tank. Thus, beads discharging from the centrifuge are able to pass directly into the treatment tank with the cyanide wash solution.

In the treatment tank, the beads are allowed to *8 9 S* 30 settle, with gentle stirring of the cyanide solution if required. In passing through the cyanide solution, metal values taken up by beads in the tailings tank are stripped from the beads. The ratio of precious metals to non-precious metals thereby taken up by the cyanide solution will depend on the selectively of the beads and, of course, the metal content of the tailings with which the beads were in contact. The height and concentration of the cyanide solution is such as to strip substantially all metal values from the beads in the time taken for the beads to settle in the treatment tank. Cyanide solution 3114L 9

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and beads are drawn from the base of the treatment tank and separated, for subsequent regeneration of the beads and recovery of precious metal values from the cyanide solution. The operation preferably is continuous, with regenerated beads being recycled to the tailings tank.

Also, after recovery of metal values from the cyanide solution, that solution is recycled to the treatment tank. The cyanide solution and beads are drawn from the treatment tank such that mechanical damage of the beads is minimised, and an eductor pipe may be used for this purpose.

The beads are regenerated by a treatment in which they are ccntacted by acid solution. Prior to contact with the acid solution, the beads preferably are washed with water to remove residual cyanide solution, with resultant cyanide containing wash solution preferably passing to the treatment tank. After contact with the acid, the beads are separated from the acid solution.

They then preferably are subjected to a further water wash, to remove residual acid. Acid solution from which .o S. the beads intitially are separated can be recycled to an acid storage tank, while the acid wash solution resulting from the further wash can pass to the tailings tank and/or to the tailings pulping tank.

Separation of the beads from the cyanide solution and the regeneration steps to which the beads are then subjected, can be conducted in any suitable device or devices. However, it again is desirable that mechanical damage to the beads be minimised. One convenient S 30 arrangement is to conduct the separation in a cyclone separator, and to conduct each of those steps in a respective centrifuge such as detailed above, with the beads passing in turn from the cyclone to a first centrifuge, and from the first centrifuge to the or each next centrifuge. The cyclone and the centrifuges may be in a vertical array, such as as a substantially co-axial array.

The regenerated beads may pass from the last of the centrifuges to the tailings tank. To facilitate this, the array of centrifuges may be mounted above that tank.

3114L 10 Thus, cyanide solution and beads discharged from the treatment tank may pass to the cyclone to extract cyanide solution which is recycled to the treatment tank, with the beads passing to a first, uppermost one of three centrifuges, each having a parabolic vessel. In the first centrifuge, the beads can be subjected to a water wash which removes residual cyanide solution. The beads to overflow the vessel of that centrifuge and pass to the second, intermediate centrifuge. In the second centrifuge, the beads can be separated from cyanide contai:-.ng wash solution, and subjected to a regenerating acid wash, with the beads overflowing the vessel of that centrifuge and passing to the third, lowest centrifuge.

In the third centrifuge, the beads can be separated from acid solution and subjected to a further water wash, with the beads overflowing the vessel of that centrifuge and then being sprayed into the tailings tank.

As indicated, the cyanide solution containing precious metals, when separated from the beads, is treated for recovery of those metals. This can be by any conventional proceedure for treatment of such solutions.

However, it preferably is by the solution being passed to a recovery unit, such as one having at least two recovery tanks so that one tank is on-line at all times, in which 25 precious metals are recovered by ion exchange resin beads which are selective for precious metals and affect a substantially complete separation of those metals from any base metals. Where recovery is by means of such selective beads, these preferably are treated in a separate, closed *0 kG S• 30 circuit for recovery of the precious metals by backwashing S"and treatment with eluting solution.

In the foregoing description, reference is made to 9**b use of a respective eductor for withdrawing beads and fresh water from the tailings tank, and for withdrawing beads and cyanide solution from the treatment tank. In S each case, the reference is to a device such as known as a water jet eductor, which utilises the kinetic energy of a pressurised liquid, such as water, to entrain a fluid, in this case, a mixture of beads and either water or cyanide solution. As will be appreciated, the pressurised liquid 3114L 11

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issues ftom a nozzle which generates a reduction in pressure in a chamber upstream from a diffuser or venturi, with the fluid being drawn into the chamber and mixing with the liquid. Thus, in the description above in relation to separation of beads from fresh water or cyanide solution, the volume of liquid from which the beads are separated is greater than that with which the beads initially were withdrawn.

In order that the present invention may more readily be understood, reference now is directed to the accompanying drawings, in which:- Figure 1 is a schematic representation of the principal components of an overall plant layout; Figure 2 is a schematic representation of a tailings tank of the layout of Figure 1; Figure 3 is a schematic representation of a centrifuge arrangement for recycling to the tank of Figure 2; Figure 4 is a schematic representation of a treatment tank of the layout of Figure 1; Figure 5 is a schematic representation of a charging and recycling system for the tank of Figure 4; Figure 6 is a schematic representation of a recovery *unit of the layout of Figure 1; S 25 Figure 7 is a schematic representation of a preferred form of centrifuge vessel for use in the plar.

of Figure 1; and Figure 8 is a sectional schematic representation of an eductor suitable for use in the plant of Figure 1.

With reference first to Figure 1, the plant layout 9 zomprises a system in which several components are duplicated, with the description being directed to only

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one half of that system. The system also includes a tailings pulping tank which can be of any suitable type, but which is not shown. An aqueous pulp of particulate tailings is pumped from the tailings pulp tank to a treatment tank 10 in which the tailings are contacted with suitable ion exchange resin beads which take up metal values in the diffused form from the pulp. After a sufficient residence time for the beads in tank 10 for 3114L 12 that take-up, a mixture of water and beads is drawn from tank 10 via eductor pipe 12, and passe- the separator/ charging device 14 of treatment tan. 16. Device 14 separates the beads from the water, with the beads then sprayed by device 14 into a cyanide solution contained in tank 16. The beads settle in tank 16, during which the metal values are stripped from the beads by the cyanide solution. The beads and pregnant cyanide solution then are withdrawn from tank 16 via eductor pipe 18, by which they pass to separator/regenerator device 20 mounted above tank 10. After regeneration, device 20 recycles the beads to tank 10. Pregnant cyanide solution also withdrawn from tank 16 via eductor pipe 18 is separated from the beads in device 20, prior to regeneration of the beads; with the cyanide solution then being passed to recovery unit 22 and ultimately being recycled to tank 16 via conduit 24.

As shown in more detail in Figure 2, tank 10, which typically is of cylindrical form, has a conical base 26 inclined downwardly to a central outlet 11 communicating with eductor 12. A short distance above base 26, tank has an inlet 13 through which an aqueous pulp of tailings S, passes via conduit 28 to manifold 30, for discharge within ,tank 10. A constant level of pulp is maintained in tank ,1 0 by supply via manifold 30, with this supply most 25 preferably being continuous and pulp discharging via an o0Q upper outlet (not shown but represented by the upper outwardly directed arrow). A resultant upward flow of the pulp is stirred islowly, such as at about 1 rpm, by paddle 32 mounted on rotatable shaft 34, driven by motor 35 (see 00 00 Figure Ion exchange resin beads pass into the pulp 00,4 00 from device 78 (see Figure which is rotated by motor 35 and drive system 36, and are gently mixed with the pulp .ogO by the action of paddles 32, to achieve intimate mixing of *the tailings and beads. The beads slowly settle through the pulp towards base 26, with the overall arrangement '"providing a sufficient residence time for the beads in tank 10 to enable the beads to take up metal values present in the tailings in the above mentioned diffused form. Between the levels of manifold 30 and base 26, tank 10 has a further inlet 37 by which fresh water is supplied 3114L 13 via conduit 38. The purpose of this is to supply a fresh water below guide plate 37a, to establish a region of fresh water below manifold 30 in which the settling beads are rinsed of adhering tailings. The fresh water region below manifold 30 serves to prevent the tailings from flowing downwards along base 26 towards outlet 11 and eductor pipe 12. Beads and fresh water are withdrawn from outlet 11 of tank 10, via eductor pipe 12, and passed to device 14 mounted above tank 16 via line 39. Inverted conical baffle 34a on the lower end of shaft 34 guide beads settling centrally in tank 10 so that they settle in the fresh water outwardly from outlet 11.

Device 14 is shown in greater detail in Figure 5 and comprises an upper part defining a receiving cyclone and a lower part comprising a centrifuge 42. A motor 44 provides drive to a vertical shaft 46 through device 14, with the shaft having paddles 48 integral therewith in cyclone 40, and parabolic centrifuge vessel 50 rotatable therewith in centrifuge 42. As seen most clearly in Figure 5, cyclone 40 has an upwardly and outwardly tapered, frusto-conical peripheral wall 40a, a frusto-conical base 40b of substantially greater cone-angle, and a central outlet 40c in base 40b by which vessel 40 communicates with centrifuge 42. Shaft 46 extends through outlet 25 while wall 40a has a lower inlet depicted by the incoming arrow and an upper outlet depicted by the outgoing arrow.

The discharge pulp withdrawn from tank 10 via eductor pipe 12 is charged to cyclone 40 via the inlet. Under the action of paddles 48, with slow rotation of shaft 46, 30 cyclone 40 functions to precipitate beads from the water by slowing the velocity of the mixture of beads and water. The beads and some water pass through outlet into centrifuge 42. The level of remaining water rises in cyclone 40 and is recycled through the upper outlet to the tailings pulping tank.

Centrifuge 42 has an outer housing 43 mounted on top of tank 16 and within which vessel 50 is rotatable with shaft 46. The outer periphery of vessel 50 is curved down around the upper edge of lower vessel 51 with the latter fixed in relation to housing 43. Below outlet 40c of 9 9 '6 6 *66 0 (6 6'61 *960 go Se *f e 0e J 4466 a 0 3114L 14

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cyclone 40, shaft 46 has a downwardly and outwardly flared baffle 52 which deflects the beads into vessel outwardly from the axis of shaft 46. The drive provided by motor 44 causes relatively slow rotation of vessel such that water is retained in vessel 50, while the beads are able to rise up the wall of vessel 50 so as to pass over the upper edge thereof. The level of water in vessel is controlled by an annular weir 50a, which excess water overflows into vessel 51. The beads are assisted in their passage to outlet 43a of housing 43 by being sprayed with cyanide solution from a circumferential array of nozzles 54 above vessel 50. Centrifuge 42 has an outlet pipe 55, by which water can be discharged from vessel 51 and recycled to the pulping tailings tank. The beads overflowing vessel 50 are able to pass through throat 43a of housing 43 to distributor 56 from which they are sprayed into tank 16 by rotation of distributor 56 under the action of motor 57 and drive system 57a.

Device 20, as shown in Figure 3, has an upper part 20 58 defining a cyclone separator similar to cyclone 40 and to which the beads and cyanide solution pass, and a lower part 59 comprising a vertical array of centrifuges *60b and 60c each similar to centrifuge 42. Associated with device 20, there is a motor 62 which, via shaft 64,

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provides drive to each centrifuge of array 60 and to cyclone 58. The supply of beads and cyanide solution to cyclone 58 is toward the lower extent of its peripheral 99 99 wall, with the cyclone operating with rotation of shaft 64 *and paddles 65 similarly to cyclone 40 such that the beads pass through opening 58a to centrifuge array 60, with the cyanide solution being discharge at the upper extent of cyclone 58 and being passed to recovery unit 22.

Each centrifuge of array 60 has a respective baffle 66a, 66b, 66c and parabolic vessel 68a, 68b, 68c similar to the deflector and vessel of centrifuge 42. The beads and some cyanide solution passing through throat 58a of cyclone 58 are received into upper centrifuge 60a and deflected by its baffle 66a into vessel 68a. Rotation of that vessel effects a separation of the cyanide solution which is extracted via line 70a and is recycled to the 3114L 15

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cyanide tank, while the beads pass over the upper peripheral edge of vessel 68a and then are washed with a fresh water shower from nozzles 72a. The beads then pass down through the opening of guide 74a so as to be distributed by baffle 66b into the vessel 68b of the second, intermediate centrifuge 60b. By similar operation of centrifuge 60b, and an acid shower from nozzles 72b, acid solution regenerates the beads which then are guided into centrifuge 60c via guideway 74b; with the liquid separated in centrifuge 60b exiting through conduit 70b by which it passes through to the tailings tank. In the third, lowest centrifuge 60c, a similar operation proceeds, using a fresh water shower from nozzles 72c, water washes the beads which then are passed by guide 74c through throat 76 and rotating distributor 78; with acid containing wash solution separated from centrifuge exiting through conduit 70c to the acid storage tank.

Under the action of distributor 78, rotated by motor and drive system 36, the beads are again sprayed into tank With reference to Figures 1 and 6, it will be seen that cyanide solution discharging from cyclone 40 is G passed to recovery unit 22 via line 79. The cyanide solution is received in upper chamber 80 of tank 82, in which it accumulates so as to overflow wier 84 and flow into lower chamber 86. Tank 82 accommodates cyanide solution received from each of the two cyclones 40. From S* chamber 86, the solution passes to one or other of recovery column pairs 88, 90. Each column pair has a first stage column 88a, 90a into which cyanide solution is 0. able to be received from chamber 86 and a second stage column 88b, 90b from which cyanide solution is received from the respective column 88a. 90a. From either column 88b, 90b, the cyanide solution is able to be returned via conduit 24 to one or other of the tanks 16. Each column of each pair 88, 90 contains beads of ion exchange resin which are selective to precious metals, such that precious metals stripped by the cyanide solution in tank 16 are taken up by the selective beads, leaving base metals in the cyanide solution. Operation with the columns of one 3114L 16 *50500

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S 0 00** eCOSO 0 pair continues until the beads therein have reached their capacity for taking up precious metals. At that stage, the columns of the other pair are brought into operation and the initial pair treated for the recovery of precious metals and regeneration of their beads by passing a backwashing solution, such as water, and then an eluting solution, through the columns. After the precious metal values are stripped from the beads by the eluting solution, that solution is treated by conventional procedures for recovery of the precious metals. Required flow through column pairs 88, 90 is controlled by valves 88c, 88d, 88e, 88f and 90c, 90d, 90e, 90f, and by valves 24a, 24b, 24c in line 24.

With reference to Figure 7, there is shown a schematic sectional view of a centrifuge vessel 100 of a preferred form. That is, Figure 7 shows the preferred form for previously described centrifuge vessel 50 of device 14, and vessels 68a, 68b, 68c of device 20. Vessel 100 has a peripheral wall 102 which is of substantially 20 parabolic formi and extends upwardly from basal section 104. However, rather than wall 102 being of that form up to its rim 106, such as shown by the broken outline and corresponding to the arrangement of vessels 50 and 68a to c, wall 102 is radially outwardly stepped a short distance below rim 106. Thus, wall 102 defines a lower portion 108 which extends over a major part of its height, a radial flange 110 which extends outwardly from the upper edge of lower portion 108, and an upper portion 112 which extends upwardly from the outer edge of the flange 110 to rim 30 106. Also, vessel 100 is of a suitable impervious material, except that wall portion 112 has a lower peripheral zone 112a which extends upwardly from flange 110 and is perforate. Zone 112a is defined by a suitable mesh, grid or the like which has openings which prevent the passage of the ion exchange resin beads therethrough.

Rim 106 curves smoothly outwardly from portion 112 of wall 102, and merges with an outwardly and downwardly inclined peripheral skirt 114. Also, at its lower extent, wall 102 merges smoothly with basal section 104, while section 104 curves upwardly and radially inwardly to merge 3114L 17 L smoothly with central cylindrical hub 116.

Hub 116 is of lesser height than parabolic wall 102, and defines a central weir which liquid charged to vessel 100 is able to overflow. Hub 116 corresponds to weir of vessel 50 of device 14, and the corresponding weir of each of vessels 68a to c of device Hub 116 defines a bore 118 through which such overflowing liquid is able to pass, with the liquid passing to a lower vessel corresponding, for example, to vessel 51 of device 14. Also, a rotatable shaft 120 extends through bore 118, and vessel 100 is rotatable with shaft 120 by means of a number of radial arms 122 inter-connecting hub 116 and shaft 120. Shaft 120 corresponds to shaft 46 of device 14 and shaft 64 of device Separation of beads and liquiq of a mixture supplied to vessel 100 generally will be understood from the description of the centrifuges of devices 14 and However, brief further description is appropriate. A 20 mixture of beads and liquid to be separated is fed downwardly into vessel 100, as the latter is rotated with shaft 120. The feed preferalby is via a conical baffle co-axially mounted on, and rotatable with, shaft 120 such that the mixture is spiralled in the direction of rotation of vessel 100 and distributed outwardly of hub 116. The rotation of vessel 110 at a suitable speed causes the beads and some liquid to move out to and up the surface of *.wall 102, while liquid in excess of that required to fill .'.vessel to the height of hub 116 overflows the latter to pass through bore 118. The beads and some liquid reach, and are accelerated outwardly across, flange 110, after which the liquid is discharged through the openings of perforate zone 112a and the beads continue to rise to, and are discharged over, rim 106.

If the parabolic form of wall 102, above flange 110, was of the form shown by wall portion 108 as continued by the broken outline, its speed of revolution w would need to be of a level substantially determined by: 2gH R, where H and R are the nominal height and radius, 3114L 18 respectively of the parabolic wall. For such vessel, increasing w ,bove that value would result in some liquid overflowing the rim, with the beads, and ineffective separation. Thus, while such vessel enables efficient separation at the indicated value, close control over the level of w is necessary.

By adopting the form shown for vessel 100, in which wall 102 is radially stepped, there is greater flexibility of operation. Substantially the same level of w needs to be attained in order that the beads will move up to, and pass over, rim 106. However, as liquid is able to be discharged through perforate zone 112a, that level of w can be exceeded over a useful operating range to increase the rate of separation. The arrangement can be such that substantially all liquid is discharged through perforate zone 112a, although it is preferred that the feed rate for the mixture of beads and liquid to vessel 100 is such that a significant proportion of the liquid is able to overflow hub 116 and be discharged via bore 118.

As shown, an annular cover 124 is mounted in relation to vessel 100. Cover 124 has a radially inner edge 124a which is spaced from shaft 120 sufficiently to enable a mixture of beads and liquid to be charged to vessel 100. At a radially outer margin, cover 124 is spaced slightly above flange 110, to provide an annular gap which meters the movement of beads across flange 110.

Similarly, the radially outer edge 124b of cover 124 is spaced slightly from the portion of wall 102 defined by zone 112a, to meter the movement of beads upwardly from flange 110. Cover 124 also minimises splashing, and can prevent a surge in the feed to vessel 100 resulting in liquid passing to rim 106.

While flange 110 is shown as horizontal, this is not necessary. Flange 110 could be inclined upwardly and outwardly from wall portion 108. Alternatively, it could curve upwardly and outwardly, and have either a concave or convex inner surface.

In the foregoing description, it is indicated that beads and fresh water are drawn from tank 10 via eductor pipe 12, and supplied to device 14 via line 14. It also 3114L 19 is indicated that beads and cyanide solution is drawn from tank 16 via eductor pipe 18 and passed to device 20 via line 19. The respective mixture of beads and liquid is drawn via each eductor pipe by means of eductor, such as eductor 130 shown in Figure 8.

Eductor 130 has an elongate housing 132 which defines a chamber 134 and has a side inlet 136 to chamber 134. For the eductor operating between tank 10 and device 14, eductor pipe 12 will be connected to inlet 136 while, for the eductor operating between tank 16 and device eductor pipe 18 will be connected to such inlet.

Housing 132 has an inlet 138 at one end which is connectable to a source of pressurised liquid, and which communicates with chamber 134 through nozzle 140. At its other end, housing has an outlet 142. The eductor connected to pipe 12 has its outlet connected to line 39, while the eductor connected to pipe 18 has its outlet connected to line 19. Pressurised liquid supplied to inlet 138 is directed by nozzle 140 as a jet which passes I. 20 through chamber 134, and through a venturi constriction 144 between chamber 134 and outlet 142. A resultant reduction in pressure is generated in chamber 134, such that the respective beads and liquid mixture is drawn into chamber 134, via the eductor pipe, with the mixture being entrained in the jet and discharging through outlet 142.

In the case of the eductor connected to pipe 12, the pressurised liquid will be fresh water while, for the eductor connected to pipe 18, the pressurised liquid will be cyanide solution.

As will be appreciated, eductor 130 enables s*a efficient transport of beads and liquid. Importantly, it minimises risk of mechanical damage to the beads, enabling them to be reused in successive cycles. However, it will be appreciated that the mixture of beads and liquid drawn from each of tanks 10,16 is entrained in the respective pressurised liquid supplied to the eductor, such that beads are separated from a quantity of liquid in each of devices 14,20 which is greater than the quantity of liquid drawn from respective tanks 10,16. As also will be appreciated, each pressurised liquid preferably will be 3114L 20 process liquid to be recycled, to obviate a progressive increase in liquid in the overall circuits.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

9**9*9 9 9 3114L 21

Claims (14)

1. A centrifuge, suitable for use In separating ion excnar ge resin beads from a process liquid, including a bowl mounted for rotation n ar upwardly extending central axis and a motor for rotating the bowl on the axis; wherein the bowl has a peripheral wall which curves upwardly and outwardly 'romr a basal section of the o1 bowl to a peripheral rim, the bowl defines an outlet cr a pl rality of outlets at a region or plurality of regions located below the rim; the curvaiure of the peripheral wall is of smoothly curved parabolic form between tls basal section and the rim; and wherein the arrangement is such that, with a feed of tnE beads and process liquid into the bowl and rotation of the bowl by operation of the motor, a separation of the beads and liquid is effected such that tle liquid d;acharges through the or each outlet and the beads are caused to move outwardly and up the peripheral wall to discharge over the rim,

2. A centrifuge according to claim 1, whereir the motor s operable to rotate the bowl at a substantially constant speed at or s'ighty in excess of a critical speed I as determined by; co 2g/R, where H is the nominal height of the peripheral wall and R is the radius of the peripheral wall at the rim.

3. A centrifuge, suitable for use in separating ion exchan ;e resin beads from a process liquid, including a bowl mounted for rotation or an upwardly extending central axis and a motor for rotating the bowl on the axis, wherein the bowl has a peripheral wall which curves upwardly and outwardly from a basal section of the bowl to a peripheral rim, the bowl defines an outlet or a plu ality of outlets at a region or plurality of regions located below the rim; the peripheral wall is outwardly stepped a short distance below the ri; to define an outwardly extending annular flange, and the peripheral wall has a iowe portion which is of smoothly curved parabolic form between the base! section ard the flange and an upper portion of similar curved form between the flange and he rim; and wherein the arrangement is such that, with a feed of ths beads and process liquid into the bowl and rotation of the bowl by operation of the moto, a separation of the bea's and liquid is effected such that the liquid discharges through the or each outlet and the beads are caused to move outwardly and up the peripheral wall to discharge over the rim, 01 OCT '96 14:3 PHILLIFS OPHOMr~iE rIT"TPICI "23.

4. A centrifuge according to claim 3, wherein the motor is operable to rotate the bowl at a substantially constant speed In excess of a critical speed I as determined by: co= gHi /R, where H Is the nominal height of the peripheral wall and Rj is the radius of the peripheral wall at the rim. A centrifuge according to claim 3 or claim 4, wherein ithe upper portion of the peripheral wall has a perforae band intermediate the flahge and the rim, the perforate band being such as to retain the beads against passage therethrough but defining an outlet allowing outward flow of the liquid therethrough. A centrifuge according to any one of claims to 51 wherein the basal 20 section of the bowl defines an outiet for the liquid.

7. A centrifuge according to claim 6, wherein the outlet defined by the basal section comprises a central weir comprising a substarlially artnular hub portion of the bowl, and wherein the weir is substantially conce itric with but of lesser height 25 than the peripheral wall.

8. A centrifuge according to claim 7, wherein the basal pection of the bowl, between the hub portion and the peripheral is internally concave so as to curve downwardly and inwardly from the peripheral wall antf the upwardly and inwardly to the hub portion.

9. A centrifuge according to any one of claims 1 to 8, wherein a deflector is mounted axially within or above the bowl for guiding the feed as it flows into the bowl. A centrifuge according to -lam 9, wherein the aeflectbr is of downwardly and outwardly flared annular form.

11. A centrifuge according to claim 9 or claim 10, wherein the deflector is operable to impart initial circuais motion to the feed flowving into the bowl, RA% 12. A centrifuge according to any one of claims to 11, wterein the rim of the Sbowl is curved outwardly from tne peripheral wall. 01 OCT '96 14:03 PHILLIPS ORMOHDE I ITZPHTP CI 9 24 13, A centrifuge according to c'aim '12, wherein the Lowl as a peripheral skirt which is inclined downwardly and outwardly from the rim.

14. A centrifuge accc-din-; to any one of claims 1 to 13, futher including spray means operable to spray tie beads with a wash liquid as the beads pass from the io bowl, A centrifuge according to clam 14, wherein the spray reans is operable to generate an annu::, certain or spr& of wash solution around and outwardly from the rim, *a *a o C C *.CC. 16, Extraction aoparatus, for recovery of gold or gold metals frcm particulate source- material such as ore, con including an extracion tank r. which a pulp comprising an of the source material is contactable with ion exchange resin beads to take up oreilous metal values from the pulp, supply regenerated beads to the tank, and discharge means o resultant process liquid containing entrained beads from the process llquid to separating means for e9paration of the bea liquid, the supply means and/or the separating means comr centrifuge according to any one of claims 1 to

17. Apparatus according to claim 16, wherein the extracti inlet for the supply of pulp to a lower region above a base o the pulp is able to fiow upwardly in the tank for discharge frorr top of the tank; a bead inlet for the supply of beads from the upper region of the tank to enable the beads to settle under pulp; and mixing means operable to stir the pulp gently for in beads and source material; and wherein the discharge mean in the base of the tank, and an eductor by which the process 33 beads are drawn from the extractor tank and passed to the se and other precious :entrate or tailings, queous suspension oeads to enable the neans for supplying erable to separate ulp and to pass the Ss from the process arising at least one on tank has a pulp Sthe tank such that a pulp outlet at the supply means to an gravity through the imate mixing of the Sincludes an outlet iquid and entrained parating means.

18. Apparatus according to claim 16 or claim 17, whereir the supply means has a plurality of centrifuges mounted in a vertically stacked array above the extraction tank, with each centrifuge of the array being in a cordance with any one of claims 1 to 15, the apparatus further includes a supply conduit by which a treatment solution having entrained recycled beads is able t be passed to the A supply means, and wherein the supply means is operable su h that the recycled 3 lu beads are separated from the treatment solution in an up ermost one of the y'/ 01 OCT '96 14:04 PHILLIPS CRMOHDE S FITZPkTPICK 9 centrifuges and, after being separated from a wash solution applied thereto in at least one centrifuge, below the uppermost one, pass into the extraction tank substantially free of liquid,

19. Apparatus according to claim 18, wherein there are thr array, and wherein the supply means is operable To pass uppermost centrifuge to an intermediate one of the centrifuge first wash solution thereto, to separate the beads from tne fi the intermediate centrifuge, to pass the beads from the lowermost one of the centrifuges by application of a sec thereto, and to separate the beads from the seccid w lowermost centrifuge prior to the beads passing into the extrac Apparatus according tr claim 18 or claim further device which is mounted above the supply mear, and wit 20 conduit communicates, wherein the cyclone device is operab separation of treatment liquid from the beads by generat treatment liquid, the cyclone device having a basal c communicates with the supply means and a rotatable paddlf settling of the beads in the cyclone device so as to pass to th 25 the outlet. ;e centrifuges in the :he beads from the 3 by application of a rst wash solution in intermediate to a ;ond wash solution ish solution in the tion tank. including a cyclone 1 which the supply e to effect a partial ng an overflow of utlet by which it operable to effect supply means via 0r -3 0 0.*0 .o 04'-3 00000

21. Apparatus according to any one of claims 16 to 20, wherein the separating i 'ens is mounted above a treatment tank and comprises a centrifuge according to any one of claims I to 16, the centrifuge of the separating means being operable to separate the beads from the process liquid prior tc passing the beads to the treatment tank for recovery of precious metal values by contact with a treatment solution such as a cyanide solution.

22. Apparatus according to claim 21, further incl.ding r cyclone which is mounted above the separating means and which receives the process liquid and entrained beads from the discharge means, whereih the cyclone is operable to effect partial separation of process liquid from tie beads by generating an overflow of process liquid, the cyclone having a basal :utlet by which it communicates with the separating means and ci roatable paddle operable to effect settling of the beads in the cyclone so a. to pass to thO separating means via the outlet with remaining process liquid. 7Ra B *'T jitL.T '9'6 14:05 PHILLIPS ORIVONDE FITZPHTR1'i 9 P. -26 s23. Apparatus according to claim 21 or ciaim 22, where[ the treatment tank has an eductor pipe by which beads settling therein are withdrawn in entraining treatment solution, and wherein the eductor communicat s with the supply means. DATED: I October, 1996 TECNAV PTY. LTD. By PHILLIPS ORMONDE FITZPATRICK Patent Attorneys per: 1 4 1 .I ABSTRACT The centrifuge is suitable for use in separating ion exchange resin beads from a process liquid. It includes a bowl mounted for rotation on an upwardly extending central axis and a motor for rotating the bowl on the axis. The bowl has a peripheral wall which curves upwardly and outwardly from a basal section of the bowl to a peripheral rim. An outlet, or a plurality of outlets, of the bowl is defined at a region or plurality of regions located below the rim. The arrangement is such that, with a feed of the beads and process liquid into the bowl and rotation of the bowl by operation of the motor, a separation of the beads and liquid is effected such that the liquid discharges through the or each outlet and the beads are caused to move outwardly and up the peripheral wall to discharge over the rim. oS 0* S S S S 55 5 SS* S 555 S 3114L 27